1. Field
One embodiment of the invention relates to a storage apparatus having a nonvolatile storage module, and more particularly to a storage apparatus having a storage module that is configured to undergo a destructive read when data is read from it.
2. Description of the Related Art
Ferroelectric RAMs (FeRAMs), such as those of the 1T1C and 1T types, are known as nonvolatile memories (or nonvolatile storage modules) that undergo a destructive read when data is read from them. Most storage apparatuses having such a nonvolatile memory have a mechanism for writing data, once read, back into the nonvolatile memory. This mechanism can therefore prevent loss of the data stored in the nonvolatile memory in spite of the destructive read.
However, if the supply of power to the storage apparatus is interrupted while the data is being read from the apparatus, at least a part of the data may be corrupted, as is described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-069790 (hereinafter referred to as Prior Art Document 1).
In view of this, conventional storage apparatuses are configured to check for data corruption resulting from the interruption of the supply of power based on error checking and correction (ECC) data that accompanies the data being read from the storage apparatus. If the storage apparatus detects a data error, it will correct the data.
However, in the conventional storage apparatus of this type, that part of the data corrupted by the interruption of power supply remains corrupt in the nonvolatile memory until an access is made to the data including the corrupt part. Inevitably, many corrupt data parts may exist in the nonvolatile memory if the supply of power is unexpectedly interrupted repeatedly. Further, the data-error check must be performed every time data is read from the nonvolatile memory. This increases the power consumption of the storage apparatus and delays the data transfer by the time required for the error check.
Prior Art Document 1 discloses a mechanism in which a control portion completes the writeback cycle of writing the data, once read, back into the nonvolatile memory (FeRAM), before a failure in power source voltage (power failure). In this mechanism, a power-source voltage sensing portion senses a power failure beforehand, thereby achieving the completion of the writeback cycle.
Jpn. Pat. Appln. KOKAI Publication No. 07-073682 (hereinafter referred to as Prior Art Document 2) discloses a save memory SM for temporarily store the data held in the ferroelectric capacitors of a nonvolatile memory (FeRAM), which should be forcedly refreshed. This save memory SM comprises ferroelectric capacitors. Prior Art Document 2 further discloses a mechanism that copies the data held in the ferroelectric capacitors to be forcedly refreshed and then temporarily holds the data, thus copied, in the save memory SM.
The FeRAMs of 2T2C type known in the art have a hardware configuration that does not undergo destructive read when data is read.
To provide such mechanisms as described in Prior Art Document 1 or 2, a nonvolatile storage module need to have a special hardware configuration. Further, any FeRAM of 2T2C type (i.e., nonvolatile storage module that undergoes no destructive read when data is read from it) needs to incorporate a special hardware configuration, too.